[Bug tree-optimization/56654] uninit warning behaves erratically (always executed block, "is" vs "may", order when walking uses)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56654

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:8a63343a744a8584a9dfcbc3817f66755baafe8a

commit r13-2261-g8a63343a744a8584a9dfcbc3817f66755baafe8a
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Aug 29 16:16:44 2022 +0200

    tree-optimization/56654 - sort uninit candidates after RPO

    The following sorts the immediate uses of a possibly uninitialized
    SSA variable after their RPO order so we prefer warning for an
    earlier occuring use rather than issueing the diagnostic for the
    first uninitialized immediate use.

    The sorting will inevitably be imperfect but it also allows us to
    optimize the expensive predicate check for the case where there
    are multiple uses in the same basic-block which is a nice side-effect.

            PR tree-optimization/56654
            * tree-ssa-uninit.cc (cand_cmp): New.
            (find_uninit_use): First process all PHIs and collect candidate
            stmts, then sort those after RPO.
            (warn_uninitialized_phi): Pass on bb_to_rpo.
            (execute_late_warn_uninitialized): Compute and pass on
            reverse lookup of RPO number from basic block index.